But for the scala-library.jar and scala-compiler.jar, I don't need define them explicitly, how can I get sbt download their sources for me? So, I don't need config it manually after generate idea project using sbt-idea-plugin.

First, forget about trying to find some “hidden” setting in your SBT project definition enabling Scala library source download! It does not exist (at least not in SBT version 0.7.x).
Rather, there are these two things you need to do in order to whip SBT into submission:

Once you have completed these steps SBT should happily download the scala-...-sources.jar files for the Scala compiler and standard library for any new project you create.To have SBT do this for an existing project, you have to manually delete the project/boot/scala-{version} directory before performing an ‘sbt update’ (SBT does not fetch additional source artifacts if the main jar is already present).

Once you have a custom sbt.boot.properties file, there are also other ways to supply it to the SBT launcher.

+1 for the link, but I want to make sure this ends up in a Stackoverflow Crative Common Data (monthly) Dump (see blog.stackoverflow.com/2009/06/…). Hence my edit, should you accept it.
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VonCDec 18 '10 at 15:21